1. Field of the Invention
The present invention relates to a light emitting device. More particularly, the present invention relates to a light emitting device where difference of brightness of pixels can be reduced when data currents having the same magnitude are applied to the pixels.
2. Description of the Related Art
A light emitting device emits a light having a certain wavelength when a predetermined current or voltage is provided to the light emitting device, and especially an organic electroluminescent device is self light emitting device.
FIG. 1 is a plan view illustrating a common light emitting device.
In FIG. 1, the light emitting device includes anode electrode layers 100, cathode electrode layers 102, pixels 104, walls 106, anode lines 108, cathode lines 110A and 110B and a driver 112.
The anode electrode layers 100 are disposed in a first direction.
The cathode electrode layers 102 are disposed in a second direction different from the first direction.
The pixels 104 are formed in cross areas of the anode electrode layers 100 and the cathode electrode layers 102.
The walls 106 are made up of insulating material, and are disposed between the cathode electrode layers 102 to separate electrically the cathode electrode layers 102.
The anode lines 108 are coupled to the anode electrode layers 100.
The cathode lines 110A and 110B are coupled to the cathode electrode layers 102.
The driver 112 combines with end of the lines 108, 110A and 110B as shown in FIG. 1, and includes a driving circuit 114.
The driving circuit 114 drives the pixels 104.
FIG. 2A is a view illustrating a circuitry of the light emitting device in FIG. 1. FIG. 2B and FIG. 2C are views illustrating process of driving the light emitting device in FIG. 2A.
In FIG. 2A, the light emitting device includes the pixels E11 to E64 and the driver 112.
The driver 112 includes a controller 200, a first scan driving circuit 202, a second scan driving circuit 204 and a data driving circuit 206. Here, data lines D1 to D6 correspond to the anode electrode layers 100 and the anode lines 108, and scan lines S1 to S4 correspond to the cathode electrode layers 102 and the cathode lines 110A and 110B.
The controller 200 controls the scan driving circuits 202 and 204 and the data driving circuit 206 using display data inputted from an outside apparatus (not shown).
The first scan driving circuit 202 transmits first scan signals to some of the scan lines S1 to S4, for example S1 and S3. The second scan driving circuit 204 transmits second scan signals to the other scan lines S2 and S4. As a result, the scan lines S1 to S4 are connected in sequence to a ground as described below.
The data driving circuit 206 has a plurality of current sources CS1 to CS6, and provides data currents corresponding to the display data and outputted from the current sources CS1 to CS6 to the data lines D1 to D6. As a result, the pixels E11 to E64 emit light.
Hereinafter, a process of driving the light emitting device will be described with reference to FIG. 2A to FIG. 2C.
Firstly, as shown in FIG. 2B, a first scan line S1 of the scan lines S1 to S4 is connected to the ground, and the other scan lines S2 to S4 are connected to a non-luminescent source having a voltage V1, wherein the voltage V1 has the same magnitude as a driving voltage Vc of the light emitting device.
Subsequently, data currents I11 to I61 corresponding to a first display data are provided to the data lines D1 to D6. In this case, the data currents I11 to I61 are passed to the ground through the data lines D1 to D6, the pixels E11 to E61 and the first scan line S1. As a result, the pixels E11 to E61 related to the first scan line S1 emit light.
Then, as shown in FIG. 2C, a second scan line S2 is connected to the ground, and the other scan lines S1, S3 and S4 are connected to the non-luminescent source.
Subsequently, data currents I12 to I62 corresponding to a second display data inputted to the controller 200 after the first display data is inputted to the controller 200 are provided to the data lines D1 to D6. In this case, the data currents I12 to I62 are passed to the ground through the data lines D1 to D6, the pixels E12 to E62 and the second scan line S2. As a result, the pixels E12 to E62 corresponding to the second scan line S2 emit light.
Pixels E13 to E63 corresponding to a third scan line S3 emit light, and then pixels E14 to E64 corresponding to a fourth scan line S4 emit light through the method described above. Subsequently, the above process of emitting light in the pixels E11 to E64 is repeated in units of the scan lines S1 to S4.
Hereinafter, a process of driving the pixels E11 to E64 will be described in detail through difference of brightness between the pixels E11 and E12.
Firstly, resistors between each of the pixels E11 to E64 and the ground will be described.
Each of the cathode electrode layers 102 has a constant width through its whole area as shown in FIG. 1. Hence, in one cathode electrode layer, resistors between the pixels E11 to E64 have the same resistances. As a result, a resistor between the pixel E11 and the ground is Rs, a resistor between a pixel E21 and the ground is Rs+Rp, and a resistor between a pixel E31 and the ground is Rs+2Rp. In addition, a resistor between the pixel E41 and the ground is Rs+3Rp, a resistor between a pixel E51 and the ground is Rs+4Rp, and a resistor between a pixel E61 and the ground is Rs+5Rp
Hereinafter, the data currents I11 to I61 having the same magnitude are assumed to be provided to the data lines D1 to D6 so that the pixels E11 to E61 have the same brightness.
The data currents I11 to I61 pass to the ground through corresponding pixels E11 to E61 and the first scan line S1. In this case, because the data currents I11 to I61 have the same magnitude, cathode voltages VC11 to VC61 of the pixels E11 to E61 are proportionate to resistor between corresponding pixel and the ground. Therefore, the values are high in the order of the cathode voltages VC61, VC51, VC41, VC31, VC21 and VC11. Here, brightness of the pixels E11 to E61 is affected by the cathode voltages VC11 to VC61 of the pixels E11 to E61. Generally, when data currents having the same magnitude are provided to the pixels E11 to E61, the higher the cathode voltages VC11 to VC61 are, the smaller the pixels E11 to E61 have brightness. Accordingly, when the data currents having the same magnitude are provided to the pixels E11 to E61, the pixel E11 related to the smallest resistor of resistors corresponding to the pixels E11 to E61 emits a light having the highest brightness. However, the pixel E61 related to the highest resistor of the resistors emits a light having the smallest brightness.
In short, when the data currents I11 to I61 having the same magnitude are provided to the pixels E11 to E61, the brightness of the pixels E11 to E61 is governed by the resistors between each of the pixels E11 to E61 and the ground.
In FIG. 2C, a resistor between a pixel E12 and the ground is Rs+5Rp. Accordingly, the pixel E12 of the pixels E12 to E62 corresponding to the second scan line S2 emits a light having the smallest brightness.
Hereinafter, the pixels E11 and E12 will be compared.
The resistor between the pixel E11 and the ground is Rs, but the resistor between the pixel E12 and the ground is Rs+5Rp. Hence, when pixels E11 and E12 are preset to have the same brightness, i.e. the data currents I11 and I12 having the same magnitude are provided to the pixels E11 and E61, the pixel E11 emits a light having brightness higher than the pixel E12. In this case, the pixel E12 is located next to the pixel E11, and so difference of brightness of the pixels E11 and E12 is sensed by a user.
In brief, in the light emitting device, though pixels are preset to have the same brightness, difference of brightness between the pixels is generated. In addition, the difference of brightness of the pixels E11 to E12 may be sensed by the user.